Digital-age Earth's signal gets weaker for 'any ETs out there'

Published on Monday 25 January 2010 20:56

SATELLITE TV and the digital revolution is making humanity more and more invisible to inquisitive aliens on other planets

That might be good news for anyone who fears an Independence Day -style invasion by little green men. But it is also likely to make the search for extra-terrestrial intelligence by Earthly scientists harder.

Speaking at the Royal Society in London, Dr Frank Drake, the world's leading ET hunter, said the digital age was effectively gagging the Earth by cutting the transmission of TV and radio signals into space.

At present, the Earth was surrounded by a 50 light year-wide "shell" of radiation from analogue TV, radio and radar transmissions, he said.

But although the signals had spread far enough to reach many nearby star systems, they were rapidly vanishing before the march of digital technology.

To a race of observing aliens, digital TV signals would look like noise, said Dr Drake. Digital transmissions were also much weaker than their terrestrial equivalent.

While old-style TV transmitters might generate one million watts, the power of a satellite signal was around 20 watts. Satellites also aimed their transmissions at the Earth, with almost none being allowed to escape into space.

"Now the actual amount of radiation escaping into space is about two watts, not much more than you get from a cell phone," said Dr Drake.

"If this continues into the future very soon our world will become undetectable. Using ourselves as an example, it means the difficulty of finding other civilisations will be much greater.

"We're going to have to search many more stars and many more frequencies."